feat(policy-ocr): store the IVA A.N.A. already prints

The parser has been reading A.N.A.'s `TAX` cell since the ANA layout landed,
but `ParsedPolicy` had nowhere to put it, so the figure only ever reached a
review note and every OCR-confirmed policy was written with `tax` null — even
though the paper states it.

`TAX` now flows parser -> `extractedTax` -> `Policy.tax`, alongside the premium
fields beside it. GMX stays null: its certificate carries no premium at all, so
there is no tax on it either.

The other two cells stay out, for reasons worth keeping:

  - `LOCAL TAX` is a separate levy with no destination column, and summing it
    into `tax` would produce an IVA that no longer divides back to a rate —
    which is the whole reason to store the figure. It reads 0.00 on every
    policy seen so far; a non-zero one now raises a note saying the total will
    not reconcile, instead of quietly inflating the IVA.
  - `DISCOUNT` has no column and prints as a bare "-" when unused, which is
    what makes the row positional rather than "find six amounts".

`taxRate` is left null by confirm. A.N.A. prints the amount, not the rate, and
back-dividing it would mint a rate the document never stated; the capture form
resolves one from the line of business instead.

The review screen gains derecho de póliza next to the new IVA field. It was
already parsed and already written on confirm, but never shown — and an IVA
with no fee beside it leaves the reviewer unable to see why premium + fee + tax
equals the printed total.

The spec's assertion moved off the note and onto the field, plus a check that
the row reconciles: 298.61 + 30.00 at 8% is 26.29, totalling 354.90. That
agreement is what proves the positional mapping landed on the right cells
rather than merely on six numbers.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

packages/database/prisma/migrations/20260818140000_policy_ocr_extracted_tax/migration.sql

@@ -0,0 +1,9 @@
+-- A.N.A. prints IVA on the policy face and the parser already read it, but
+-- `ParsedPolicy` had no field for it, so the figure only ever reached a review
+-- note and the confirmed Policy was written with `tax` null. This gives it a
+-- column, matching the premium fields beside it.
+--
+-- GMX stays null: its certificate carries no premium at all, so there is no
+-- tax on it to read either.
+ALTER TABLE `policy_ocr_documents`
+  ADD COLUMN `extractedTax` DECIMAL(12, 2) NULL;

packages/database/prisma/schema.prisma

@@ -503,6 +503,11 @@ model PolicyOcrDocument {
   extractedNetPremium         Decimal?  @db.Decimal(12, 2)
   extractedPolicyFee          Decimal?  @db.Decimal(12, 2)
   extractedBrokerFee          Decimal?  @db.Decimal(12, 2)
+  /// IVA off A.N.A.'s `TAX` cell. Null on GMX, whose certificate carries no
+  /// premium at all. The adjacent `LOCAL TAX` is a separate levy with no
+  /// column of its own and is NOT summed in — it would make the figure stop
+  /// dividing back to a rate; the parser reports a non-zero one as a note.
+  extractedTax                Decimal?  @db.Decimal(12, 2)
   extractedTotal              Decimal?  @db.Decimal(12, 2)
   /// Per-coverage rows from the GMX "Material damages" / "Additional risk"
   /// tables and ANA's numbered risk sections — preserved verbatim so a